In recent years, much attention has been paid to organic electronic element, including organic EL element, organic solar cell and so forth, configured by stacking an organic functional layer on an anode using a transparent electrode, and further stacking thereon a cathode. The transparent electrode is understood as an essential constitutive technology in these sorts of elements.
Conventional transparent electrode most popularly used is ITO transparent electrode for its advantages in electro-conductivity and transparency, in the form of a film obtained by depositing, on a transparent substrate, indium-tin composite oxide (ITO) by vacuum evaporation or sputtering.
The ITO-based electrode produced by vacuum evaporation or sputtering, however, suffers from low productivity due to single-substrate-oriented nature of these processes, and poor adaptability to large-area element. The ITO-based electrode which is intrinsically less flexible is also not applicable to elements required to be flexible. In addition, the transparent electrode used for the organic electronic elements has been demanded for larger area and lower resistivity, so that the resistivity of the ITO transparent electrode has been proven to be insufficient.
Therefore in place of the ITO electrode, there has been proposed a transparent metal electrode using metal nano-particle or CNT, and a transparent polymer using conductive polymer.
The transparent metal electrode, however, has a rough irregularities on the surface thereof, makes it difficult to form thereon a thin hole injection layer, and possibly causes current leakage.
Meanwhile, the transparent polymer electrode, when formed thereon with the hole injection layer, may swell and re-dissolve. This may unfortunately produce dark spot in the organic EL element, and may reduce efficiency due to increase in interface resistance.
To address these problems, there have been proposed structures each having a patterned metal conductive layer and a conductive polymer layer stacked thereon (see Patent Literatures 1 and 2, for example).
These structures have the metal conductive layers smoothened, thereby the current leakage may be suppressed to achieve a uniform conductivity over the plane. The conductive polymer, however, shows a large absorption in the visible light region, so that it is difficult for the transparent electrode to balance the transparency and conductivity.
Aiming at improving the efficiency and reducing the operating voltage of the element, there have been other proposals to use conductive polymers doped with a fluorinated polymer acid for a buffer layer such as the hole injection layer (see Patent Literatures 3, 4 and 5, for example).
While these materials, having large work functions, could improve the hole injection function, they need a buffer layer for facilitating hole injection, preliminarily formed on the transparent electrode typically composed of ITO, and need be formed thinly and uniformly, raising problems of low productivity and large variation in performance of the element.